This invention relates to a specific metal oxide having uniform micropores, the process for producing said metal oxide and the catalyst carrier comprising said metal oxide. More particularly, the invention relates to various metal oxides having a very narrow pore size distribution in the micropores region within the range of between 10 and 100 Angstroms, in which the pore size of these metal oxides is slightly larger than that of Y-Zeolite which is the largest in crystalline aluminosilicates, the process for producing the above described metal oxides and the catalyst carriers comprising the metal oxides.
A number of industrial materials having the pores size of between some and a few thousands Angstroms such as an adsorbent, an ion exchange material and a catalyst are vastly used and noted. For example, metal oxides such as .gamma.-alumina and silica gel are important inorganic materials: these metal oxides are widely utilized as a catalyst carrier, an adsorbent of water, an adsorbent of gaseous organic compounds and inorganic compounds and so on. Mixed metal oxides are also important inorganic materials because they have high acidic property. Herein, each metal oxide as a constituent component of mixed metal oxides does not have such high acidic property. It is well recognized that the structure of carriers, especially, the pore size is a very important factor in preparing a catalyst having high catalytic activity: it is well known that the pore size affects strongly catalytic activity, selectivity and catalyst life in catalytic reactions. It has become apparent that the pore size of the macropores, defined as the pores having more than 100 .ANG. also affects strongly catalytic activity, selectivity and catalyst life, in connection with diffusion, contact area and other factors. However, it is well known that the pore size of the micropores, defined as the pores having less than 100 .ANG. is a more important factor of catalytic activity and selectivity than the macropores. Especially crystalline aluminosilicates having the pore sizes within the range of between 4 and 11 Angstroms, called "Molecular sieve", is characterized by having uniform micropores and is known as a shape selective catalyst which is used for various syntheses such as the synthesis of hydrocarbons, cracking of linear hydrocarbons and alkylation of aromatic compounds. On the other hand, porous materials having a uniform pore size are expected to have the intimate relationship to various industrially and technologically important properties. However it has not been reported yet that an amorphous metal oxide having substantially uniform micropores can be prepared.
Several methods on controlling the micropore structure of a carrier, a catalyst or a mixture of them have been reported. Taniguchi et al. [Bulletin of the Japan Petroleum Institute, 13 (2), 147 (1971)] described the effect of the following preparation conditions on the pore structure of alumina; pH of the reaction solution, the concentration of starting materials in gelation, the acid treatment of alumina hydrates and the alcohol treatment of alumina hydrates such as boehmite gel. Baswadian et al. [J. Catal. 1, 547 (1962)] also described the effect of the addition of various substances such as water-soluble or dispersed organic polymers, a volatile salts or sulfur to alumina and silica gel, on the pore structure of these oxides. The above oxides obtained by the addition of water-soluble organic polymers such as polyethylene glycohol, polyvinyl alcohol, methyl cellulose and polyethylene oxide to hydrous gels of the above oxides have a very wide distribution of the pore diameter from 20 to 10000 Angstroms. Thus, a carrier or a catalyst having a very narrow pore size distribution within the specific range can not be easily obtained by a conventional process, as can been seen in the above mentioned references.